Membranous Organelles

Question 1

Describe lysosomes.

Answer 1

Small organelles inside the cytoplasm of almost all types of cells.

Diameter about 0.2-0.7 μm
Contains acid hydrolases.

Membrane is internally protected by high glycosylation of internal protein.

Question 2

How can lysosomes be distinguished from other vesicles in the cytoplasm?

Answer 2

Using fluorescent molecules, e.g. Luciferin yellow. They emit different coloured lights depending on pH.

Within the lysosomes the pH is acidic (<5); the colour (red in this case) will identify lysosomes.

Alternatively, we can also use colours that highlight the cytochemical activity of acid hydrolases.

Question 3

What histochemical staining procedure can be done to visualize lysosomes?

Answer 3

TEM: We can take advantage of enzymes. E.g. alcohol in phosphatase present in lysosomes that will react and remove the phosphate group.

Phosphate creates insoluble molecules, forming black spots under TEM.

LM: The same technique as TEM. Once the reaction has taken place, substrates can be visualized through specific colouring. E.g. coloured precipitates.

Can also be visualized through immunoflourescence for specific molecules.

Question 4

What is inside lysosomes?

Answer 4

Lysosomes are filled with hydrolytic enzymes.

Question 5

How is the acidity inside lysosomes maintained?

Answer 5

ATP pump pumps hydrogen ions inside to maintain low pH.

Question 6

What are lysosomes formed by?

Answer 6

Lysosomes are said to be formed by the golgi apparatus.

Question 7

Describe the chracteristics of the membrane of lysosomes.

Answer 7

Their membranes contain a high amount of cholesterol and have unique lipids.

Question 8

Describe autophagy.

Answer 8

When parts of cells not needed, e.g. mitochondria, they are wrapped by membrane of the ER aand fuse with the lysosome for digestion.

Question 9

What are the chracteristics of lysosomal storage diseases?

Answer 9

Characterized by lack of functional enzymes, consequently insoluble products accumulate inside cells.

Question 10

How many disorders of lysosomal storage diseases are there?

Answer 10

49

Question 11

Describe cause of Tay-Sachs disease.

Answer 11

Lacks enzymes beta-N-acetylhexosaminidase, accumulates gangliosides GM2 in the CNS.

Question 12

Describe cause of Gaucher disease.

Answer 12

Lacks the enzyme glucocerebrosidase, accumulates glucocerebrosidase (glycolipids) in the spleen and the CNS.

Question 13

Describe cause of Niemann-Pick Syndrome disease.

Answer 13

A missense mutation leading to defect in the sphingomyelinase (sphingomyelin).

Question 14

Why does proteins of lysosomes seem to be involved in many mechanisms?

Answer 14

Because they are highly glycosylated.

Question 15

What are peroxisomes?

Answer 15

Organelles thay are present in every cell, but especially livers and kidneys.

Also called microbodies because they are quite small - 0.6-0.7 μm.

Question 16

Describe the structure of peroxisomes.

Answer 16

They are spherical in shape, with a thickened central structure called nucleoid in their inner matrix.

Question 17

What are the functions of peroxisomes?

Answer 17

They are the site of synthesis and degradation of H2O2, a highly reactive and toxic oxidizing agent.

Microbodies are the location of ꞵ-oxidation of fatty acid chains, particularly those with a long chain (24-26 C atoms), with the possible formation of acetyl-coA, which can go back into the cytosol to be used in biosynthetic reactions.

Question 18

What molecules are contained in peroxisomes?

Answer 18

Contains about 40 oxidative enzymes (urate oxidase, D-amino acid oxidase, etc…) and catalase.

Question 19

How can peroxisomes be visualized?

Answer 19

Can be visualized using enzymes in their lumen. E.g. Diamminobenzidine (DAB), oxidized by catalase, allows microbodies to be observed with a TEM.

Question 20

Describe Zellweger syndrome.

Answer 20

Characterized by reduction/absence of functional peroxisomes in the cell (abnormalities in the liver, kidney and nervous tissue)

Question 21

Describe Neonatal adrenoleukodystrophy.

Answer 21

Disorder of fatty acid beta oxidation resulting in long chains of fatty acids in tissues throughout the body. This most severely affects myelin in the CNS.

Question 22

What treatments can be applied for peroxisome related diseases?

Answer 22

No universal cure
Not all treatment works for each patient.
Eating a diet low in long chain fatty acids or taking special oils can delay onset of disease.
Steroid can help treat adrenal dysfunction.
Bone marrow treatment which is still an experimental treatment.

Question 23

How do peroxisomes originate?

Answer 23

Division

Question 24

How does peroxisomes carry out its functions?

Answer 24

Enzymes inside perform a variety of detoxification processes.

Some use molecular oxygen to remove hydrogen atoms from specific organic substrates with hydrogen peroxide production.

Catalase decomposes hydrogen peroxide into water or is utilized to oxidize other organic compounds.

Question 25

Describe the structure and size of mitochondria.

Answer 25

Rod/ovoid shaped.

Similar size to bacteria - diam 0.5-1μm, length 1-6μm.

They can be spherical or very elongated.

They are surrounded by 2 layers of membrane - inner and outer membrane.

Question 26

What are the functions of mitochondria?

Answer 26

ATP production
Heat production
Central integration of apoptotic stimuli
Stock Ca2+ exchange
Part of cholesterol synthesis
Part of the heme synthesis of hemoglobin.

Question 27

How can mitochondria be visualized?

Answer 27

Specific immunofluorescence can be used against typical proteins of the mitochondria.

Question 28

Describe mitochondria in muscle cells.

Answer 28

In muscle cells they are arranged next to myofibrils which are main motors for contraction and therefore need ATP.

Question 29

Describe mitochondria in sperm cells.

Answer 29

In the tails of sperm cells, mitochondria are very elongated and located just below the nucleus. Provides energy to the tail for movement of spermatozoa.

Question 30

Describe the membranes of mitochondria.

Answer 30

The outer membrane allows passage of small molecules, while the inner membrane is selectively permeable and folded in extroflexions called mitochondrial cristae that increases surface area.

Question 31

WHat are the 2 types of cristae?

Answer 31

Flat (neurons) or tubular (cells that produce steroid hormones).

Question 32

Whats inside the mitochondrial matrix?

Answer 32

It contains hundreds of enzymes, DNA molecules and tRNAs; numerous ribosomes are coated on the inner membranes and are smaller than the cytoplasmic ones (70S).

Question 33

What does mitochondrial DNA consist of?

Answer 33

Consists of 37 genes coding for:
2 ribosomal RNA
22 transfer RNA
13 proteins that are part of the enzyme complexes are deputies to oxidative phosphorylation.

In each mitochondria there are between 2 - 10 copies of DNA.

Question 34

Why is mitochondria inherited from the mother?

Answer 34

This is because during fertilization, the mitochondria on sperm will not penetrate the oocyte (although it seems that a small number can). Therefore the mitochondrial genome of offspring will mostly be the same as the mother.

Question 35

Describe the Kreb’s Cycle (simplified).

Answer 35

The pyruvate enters into mitochondria where its converted by an enzyme complex called pyruvate dehydrogenase to acetyl coA which starts the Kreb Cycle.

During the Krebs cycle pairs of high energy electrons become available.

The pairs of high energy electrons are captured by 3 coenzyme NADH and 1 FADH (reduction) and taken to the respiratory chain enzymes.

During the cycle 1 GTP molecule is also produced that is then used by the cell or transformed directly to ATP.

Question 36

Describe the Electron Transport Chain.

Answer 36

The respiratory enzymes accept electron pairs (decreased) by NADH and FADH2 (which is oxidized) and utilize the energy to actively transport H+ from the mitochondrial matrix to the intermembrane space.

Each electron passing through the respiratory chain enzymes lose energy until they are taken from 2 protons H+ that are joined to ½ of O2 atoms to form 1 molecule of H2O.

Question 37

Describe ATPase.

Answer 37

Can be described as a structure formed by 2 complexes - F1 and F0.

F1 protruding in the lumen of the matrix helps form the ATP.

Question 38

How can heat be produced during ATP synthesis?

Answer 38

The production of heat is caused by the decoupling between the proton gradient and the synthesis of ATP.

The brown adipose tissue is rich in a protein called uncoupling thermogenin, formed by 2 subunits which facilitates the protons to enter into the mitochondrial matrix leading to the production of heat.

Question 39

What is the function of ATPase?

Answer 39

The gradient of protons H+ formed in the chamber is used by the outer mitochondrial ATPase complex to generate the energy needed for the reaction: ADP + P = ATP.